Although the discussion of reliability presented here is based
in part on a limited amount of system field data, the bulk of the supporting
data came from specific stress tests. The emphasis of this stress testing
relates to the integrity of the solder joints attaching the LCCs to the MIBs
and the ability of the MIBs to withstand the effects of moisture. Other areas
of stress testing covered are salt fog, shock and vibration, and temperature,
as well as long-term operation.
The relationship between stress tests and the potential primary
failure mechanisms of electronic assemblies are shown in Table
The concerns that have arisen with the arrival of LCC assembly
to MIBs have led to extensive testing to validate the concepts and the
procedures. It is difficult to establish valid acceptance criteria for short
term testing when the ultimate application is for 10 to 20 years of reliable
operation. One solution is to compare the short term performance of the new
process in accelerated tests to the performance in the same tests of older
processes that have a long history of acceptable performance.
Unfortunately, little testing of the DIP/flatpack MLB assembly
method has been done to the stringent levels currently deemed necessary for
the new assembly methods. This has made it difficult to provide a solid
comparison. Some testing has been done in which matched sets of assemblies
using both old and new processes have been run side by side to provide this
frame of reference.